In the field of ready-meals there are several known packages suitable to be put into an apparatus, in particular an oven, apt to elevate the temperature of the packaging and of the food product contained therein.
Such known packages differ one another mainly for their suitability to a thermal treatment in a specific type of apparatus (microwave oven, conventional oven, over for accelerated baking or other).
The prior art packages intended for the above described use are generally made at least partially of a plastic material, or they are completely laminated, in the portion contacting the food product, with materials such as cellophane or regenerated cellulose. These latter materials are provided with properties of thermal resistance and impermeability via a coating of thermoplastic polymers such as e.g. PVDC (polyvinylidene chloride), acrylic polymers and the like, that, in fact, attain impermeability to fat, liquids and vapors. In this way, the packaging remains suitably stiff from a structural standpoint, at the same time preserving the organoleptic properties of the food product during transportation, distribution and shelf life.
The use of the above described plastic and cellulosic materials results in an intrinsic barrier to water vapor; because of this, breathability, and in particular the necessary evacuation of water vapor during the heating process, is obtained via micro- or macro-apertures formed in the packages. In a few known packages such apertures are active, for gas exchange, only during the baking process.
However, the provision of apertures endangers product integrity, exposing it to a risk of contamination by external agents.
Moreover, the packaged product may come out from such apertures, in particular when it is, wholly or partially, in a liquid state, with the consequent possible soiling of the appliance used for heating/baking.
Also, these apertures let all the odors deriving from the food heating/baking process be released in the surrounding environment.
It is also to be noticed that the direct ejection of water vapor trough the apertures, caused by the temperature increase, inevitably carries other substances, like vaporized fats. These latter substances, by depositing on the walls of the heating appliance, cause dirtiness and produce, as a result of the carbonization of the fat substances, (further) undesired odors in the surrounding environment.
Furthermore, many existing packages are configured essentially as wrappings. Therefore, they are suitable for packaging solid/rigid food products only and, in any case, due to their inherent and necessary flexibility, they do not facilitate product consumption by the final user, despite being conceived as ready-meal enclosures.
On the other hand, prior art casings made entirely of a fibrous material, in particular paper, that is a breathable material, require sealing of their margins by adhesives, which are of an essentially thermoplastic nature. Generally speaking, during heating of the food product the temperature and pressure conditions that are established in the package bring such adhesives at or near their softening point. Consequently, the casing tends to open in the oven, which is, of course, very much undesired, considering the potential contamination to which the food products contained in the same package may be exposed during the heating/baking process and, as previously mentioned, with the consequent possible dirtying of the appliance. Besides to this, also in this case a failure in the integrity of the seals can cause a dispersion of undesired odors in the surrounding environment and the already mentioned outflow of fat substances.